Integrated atom density measurement in a zirconium atomic beam generated using a high-power strip electron beam source by diode laser absorption technique

Abstract

Strip electron guns, capable of generating two-dimensional (length⪢width) evaporating sources, are used for the application of electron beam assisted physical vapour deposition to metallurgical coating of large substrates. The collisional relaxation processes in the atomic vapour generated using such a 2D-source differ significantly from those in a point source created using axisymmetric electron gun. In order to study the influence of collision processes, an atomic beam of zirconium was generated using a 130-mm-strip electron gun and its ground electronic state population was measured in a given optical path length using a tunable diode laser based on-line absorption spectroscopic technique. These measurements were carried out as a function of vertical height from the source (114mm×6mm) and for different source temperatures obtained by varying electron beam powers in the range of 40–91kW.While the experimental values of integrated atom number density were observed to match very closely with those given by reported vapour flow model at low evaporating source temperatures, they showed significant deviation at high temperatures. The results are interpreted in terms of the collisional processes in the vapour stream and indicative of the fact that the vapour expansion from 2D source never runs out of collisions.